drewett



(No Model.)

2 Shqsets-Sheet 1.

W. A. DREWETT. DIRECT AUTING ENGINE.

Patented Aug. 15, 1 893.

attomzw I UNITED STATES PATENT OFFICE.

WILLIAM A. DREWETT, OF BROOKLYN, NEWYORK, ASSIGNOR TO MARSHALL T-.DAVIDSON, OF SAME PLACE.

DIRECT-ACTING ENGINE.

SPEGIFIGATION forming part of Letters Patent No. 503,231, dated August15, 1893. Application filed October 11, 1892. Serial Ha t 8,507. (Nomodel.)

To all whom it may concern:

Be it known that I, WILLIAM A. DREWETT,

Brooklyn, Kings county, New York, have in vented certainnew and usefulImprovements in Direct-Acting Steam-Engines, of which the following is aspecification.

My invention relates to direct acting steam engines, and more especiallyto that class of engines adapted for operating pumps, and it has for itsobject to provide means whereby the valve-pistons of the engine shall bemore perfectly balanced, and can consequently be operated more easilyand readily, and to these ends my invention consists in the features ofconstruction and arrangement substantially as hereinafter pointed out.

' Referring to the accompanying drawings, Figure 1, is a longitudinalvertical section through the steam cylinder and valve mechanism. Fig. 2,is a vertical transverse section on the line 22 Fig. 1; and Fig. 3, is ahorizontal section through the valve mechanism on the line 3-3 Fig. 1.

My invention relates especially to .direct acting engines in which isused what is known as the Davidson steam valve, and I have illustratedmy invention in connection with sufficient of the Davidson steam pumpand pumping engine to enable those skilled in the art 'to understand itsconstruction and operation.

This valve is arranged to be oscillated mechanically, to then bereciprocated or moved longitudinally a sufficient distance to close inorder that its construction may be better understood, I will describebriefly the general characteristics of the Davidson valve and engine.

The steam cylinder A, which is shown only partially, is provided withthe piston P, the

'piston rod P, which is connected with the pumping apparatus not shownherein. Mounted on the steam cylinder is the steam chest 0, receivingsteam from the pipe 13, and containing a valve D. This valve is shown asa D-shaped valve having pistons E, E, which may be formed integral withthe valve or connected thereto in any desired manner. The under side ofthe valve is recessed as at f, to form an exhaust port communicatingwith the main exhaust passage F formed in the casting of the steamchest, and the spaces g, 9 between the ends of the valve and the pistonsoperate as ports to communicate with the main piston ports G, G of thesteam cylinder. The steam chestis also provided with valve piston portse, e which extend longitudinally of the steam chest from a point aboutthe center thereof to near the opposite ends, and these valve pistonports are arranged on opposite sides of the lower portion of the steamchest as seen in Figs. 2 and 3, and have openings communicating with thechest at each end. The arrangement of these ports is best indicated indotted lines in Fig. 3, and it will be seen that the valve is providedwith ports or recesses d, d, in its sides which can be brought incoincidence with the openings of the valve piston ports.

In the Davidson engine the valve D, is provided with a pin H, whichextends into the exhaust port F, and also mounted in the exhaust port isa cam I, to which is connected the arm I, and this in turn is connectedby suitable mechanism, as a link 1 to the piston rod, so that as thepiston moves, the valve D, is mechanically oscillated to open and closethe valve piston ports, and is partly thrown longitudinally so as toproduce a closure of the main piston ports, and the further longitudinalmovement of the valve in the steam chest is accomplished by the steampassing through the ports e, e, and acting on the pistons. Thus it willbe seen that the valve has first an oscillating movement producedmechanically, then a longitudinal or reciprocating movement alsoproduced mechanically, and finally a further longitudinal movementproduced by steam pressure. This operation will be readily understood byreferring to Fig. 1, wherein the parts are shown with the main pistonport G, as partially open to the passage of steam to the steam cylinder,while the port G, is partially open to exhaust from the cylinder, andthe piston is shown in the position near to the end of its stroke, andthe cam I, has oscillated the valve and moved it longitudinally, so asto nearly close the steam passages, and, as the piston advances farther,these passages will be completely closed by the mechanical action of thecam. The oscillation of the valve has in the meantime opened the valvepiston port 6, so that the steam will pass behind the valve piston E,and at the same time the valve piston port c has been opened, so as toexhaust from the steam chest in front of the valve piston E, and it willbe readily understood that under these conditions the valve will bethrown over to its fullest extent by the direct pressure of the steam,and the main piston port G will be opened for steam, and the port G toexhaust. It will be observed that in the operation of this valve afterit has been reciprocated to its extreme movement in one direction, thesteam which accomplished this reciprocation remains in the steam chestat the opposite end of the valve as the valve piston ports are closedwhen the valve is in its extreme position. As a consequence of this whenthe cam I, is brought in contact with the pin H, to oscillate and movethe valve to close the main piston ports, this steam acts in oppositionto the movement of the valve, and especially when the engine is runningunder a comparatively high pressure of steam and running somewhatrapidly, the steam in the ends of the steam chest outside the pistonshas little time to condense, and it exerts its fullest pressure on thevalve, which has to be overcome by the cam in moving the valve. Not onlythis, but as the valve is moved, the pressure of the steam in beingcompressed, increases and offers still further obstruction to themovements of the valve which has to be overcome by the cam. It has beenfound that this causes considerable wear on'the cam and pin, as well asbeing a wastage of power, and it is with a view of preventing thiswastage and wear that my present invention is made. It may be observedthat this pressure is in opposition to the mechanical movement of thevalve, for by the time that this movement is accomplished, the valvepiston ports are opened so as to admit steam at one end of the valveagainst one piston and exhaust from the other. In order to accomplishthis object, I provide the valve piston with what may be termed a venthole or holes, andI have shown in the accompanying drawings the pistonsE, E, as provided with one or more vent holes Z, Z, extending from theirouter faces to their inner faces, their outer portions preferably beingenlarged, while their smaller or contracted portions are on the insidesof the pistons. It will be seen that in this construction the valvepistons are practically balanced, by the steam pressure beingsubstantially equal on all sides, the steam passing through the ventholes with sufficient rapidity to produce this balance, so that there ispractically the same pressure on each piston head, and when the valve isoperated mechanically itis only necessary to exert sufiicient force onthe valve to overcome the friction of the valve, resulting in less wearon the cam, and of course less force being required to move it. Afterthe valve has been mechanically moved, in order to complete its movementby steam pressure, instead of admitting steam behind the moving valve asin the former instance, I so arrange the valve piston ports that theoscillation and partial reciprocation of the valve shall open the portor ports in the valve chest in front of the moving valve to the exhaust,which will quickly reduce the pressure of the steam in this-chamber, andallow the pressure of the steam at the op posite end of the valve tomove it to open the main piston ports. It will be observed that whenthis exhaust port is opened, the vent or vents in the forward piston arealso opened, but I make the exhaust port sufficiently large to reducethe pressure of steam, and allow the valve to move the required distancebefore the steam can pass through the vent holes to produce the balance,but as soon as the valve has moved its complete distance, it closes theexhaustport, and then the steam will pass through the vent holes andrestore the balance ready for the next operation. Thus in. the positionshown, the port e, in front of the piston E, is arranged to connect withthe exhaust f, F, and this can be readily accomplished without changingthe structure and arrangement of the valve proper of the Davidsonengine, by simply omitting the steam ports and retaining the exhaustports in the valve.

While I have shown my invention as applied to the ordinary Davidson pumpin which the valve and pistons are made separately and secured together,it is obvious that it can be used in other forms of valves, as where thevalves and pistons are made integral or are otherwise combined, and morethan that, it is also obvious that this improvement may be used inconnection with other means for op erating the valve as described forinstance in my applications, Serial Nos. 448,508 and 448,500, filed oneven date herewith, and I do not therefore limit myself to the preciseconstruction and arrangement of parts shown in the drawings.

While I am aware that it is not broadly new to provide vent holes invalves and other similar devices, I am not aware that they have beenarranged in any mannersimilar to that shown and described by me, nor foraccomplishing the purposes and objects of my invention.

What I claim, therefore, is-- 1. Inapumping engine in combination with asteam chest, of a valve mounted therein adapted to be oscillated andpartially reciprocated mechanically, and to be further reciprocated bysteam pressure, the valve being provided with vent holes whereby it isbalanced on all sides, substantially as described.

2. In a pumping engine the combination with the steam chest, of a valveand pistons mounted therein,'the pistons being provided with vent holes,the valve piston ports extending from either end of the chest to aboutthe center thereof, and controlled by the valve, to substantially asdescribed.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

' WM. A. DREWETT.

WVitnesses: I

JOHN LOWE, GEO. O. ESKHOLME.

